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https://issues.apache.org/jira/browse/HDFS-4292?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13528186#comment-13528186
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Todd Lipcon commented on HDFS-4292:
-----------------------------------
I'm a bit hazy on this code, having not looked at it for a little while. So, I
had to write out some notes for myself, which I'll include here for anyone else
who wants to follow along.
The explanation of these variables is that {{firstChunkOffset}} represents the
byte offset of what the DN will start sending, and {{startOffset}} is the byte
offset that the client has requested. Then {{checksum.getBytesPerChecksum()}}
is the 'checksum chunk size', typically 512 bytes. So, for example, if the
client wanted to read starting at byte 1026, we would have:
- {{firstChunkOffset == 1024}} (since the DN always aligns backwards to the
beginning of a chunk)
- {{startOffset == 1026}}
- {{checksum.getBytesPerChecksum() == 512}}
The new logic says that if {{firstChunkOffset <= (startOffset -
checksum.getBytesPerChecksum())}} it is an error -- in other words, that the
{{firstChunkOffset}} should be no more than a single chunk backward from the
requested start offset. That seems right to me.
So, +1. I'll commit this momentarily
> Sanity check not correct in RemoteBlockReader2.newBlockReader
> -------------------------------------------------------------
>
> Key: HDFS-4292
> URL: https://issues.apache.org/jira/browse/HDFS-4292
> Project: Hadoop HDFS
> Issue Type: Bug
> Reporter: Binglin Chang
> Assignee: Binglin Chang
> Priority: Minor
> Attachments: HDFS-4292.patch
>
>
> {code}
> if ( firstChunkOffset < 0 || firstChunkOffset > startOffset ||
> firstChunkOffset >= (startOffset + checksum.getBytesPerChecksum())) {
> {code}
> should be:
> {code}
> if ( firstChunkOffset < 0 || firstChunkOffset > startOffset ||
> firstChunkOffset <= (startOffset - checksum.getBytesPerChecksum())) {
> {code}
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